Thermographic technology is well known. In thermographic recording elements having a photosensitive layer on a support, exposure is made to form latent images which are converted into visible images through heat development. The technology is disclosed, for example, in U.S. Pat. Nos. 3,152,904 and 3,457,075, D. Morgan and B. Shely, "Thermally Processed Silver Systems" in "Imaging Processes and Materials," Neblette, 8th Ed., Sturge, V. Walworth and A. Shepp Ed., page 2, 1969.
This technology well complies with the recently increasing social demand for simple processing and environmental protection.
In prior art photothermographic elements, photosensitive layers are formed by applying coating solutions based on organic solvents followed by drying. For example, U.S. Pat. No. 5,415,993 discloses a system of polyvinyl butyral as a binder in toluene and methyl ethyl ketone as a solvent. The use of organic solvents, however, is undesirable from the ecological and safety standpoints. One countermeasure which has been proposed is a technique of forming photosensitive layers using aqueous solvents. In connection with the aqueous coating of photosensitive layers, JP-A 116114/1978, 151138/1975 and 28737/1983, for example, disclose to use gelatin, polyvinyl alcohol, and polyvinyl acetal as the binder, respectively. These systems, however, fail to achieve satisfactory photographic performance. There is a demand to have a photothermographic element that is formed without using organic solvents which are undesirable from the ecological and safety standpoints, and the exhibits satisfactory photographic performance.
In general, the commodity value of photothermographic elements becomes very low if the adhesion between the photosensitive layer and the support is insufficient because images can be separated and lost on use. Therefore, there is a demand to have a photothermographic element that is formed using aqueous coating solutions and free of such drawbacks.